makefile

@@ -1,5 +1,5 @@
 CC = i386-elf-7.5.0-Linux-x86_64/bin/i386-elf-gcc
-CFLAGS = -ffreestanding -g -Wall -Wextra -Wno-builtin-declaration-mismatch -mno-sse -mno-mmx -mno-avx -march=i386 -c -I src/
+CFLAGS = -ffreestanding -g -Wall -Wextra -mno-sse -mno-mmx -mno-avx -march=i386 -c -I src/
 LD = ld
 LDFLAGS = -T link.ld -melf_i386
 AS = nasm

src/kernel/initrd.c

@@ -232,7 +232,7 @@ void* load_file_from_initrd(uint8_t* initrd, const char* filename)
 	void* file_content = tar_get_file_content(file);
 	memcpy(file_data, file_content, file_size);
 
-	printf("Loaded '%s' at 0x%x, size=%u\n", filename, (unsigned int)file_data, file_size);
+	printf("[initrd] Loaded '%s' at 0x%x, size=%u\n", filename, (unsigned int)file_data, file_size);
 
 	return file_data;
 }

src/kernel/kheap.c

@@ -6,6 +6,7 @@
 #include "kheap.h"
 #include <stdint.h>
 #include "system.h"
+#include "../libc/stdio.h"
 
 // Free list allocator
 
@@ -17,6 +18,7 @@ void init_alloc()
 	free_list = (block_t*)heap;
 	free_list->size = HEAP_SIZE-sizeof(block_t);
 	free_list->next = NULL;
+	printf("[kernel] initialized heap and allocator, start=0x%x\n", heap);
 }
 
 void* malloc(size_t size)

src/kernel/kheap.h

@@ -17,7 +17,6 @@ typedef struct block
 
 #define HEAP_SIZE 1024*1024	// 1MB malloc-able
 
-
 void init_alloc();
 void* malloc(size_t size);
 void free(void* ptr);

src/kernel/kmain.c

@@ -123,9 +123,9 @@ void kmain(multiboot2_info *mb_info)
     void* binary_file = load_file_from_initrd((uint8_t*)initrd_addr, "./hello.bin");
     if (binary_file == NULL)
     {
-	printf("NOT LOADED...\n");
+	printf("[debug] Failed to load test program!\n");
     } else {
-	printf("LOADED!\n");
+	printf("[debug] Test program loaded!\n");
     }
 
     void (*program_entry)() = (void (*)())binary_file;

src/kernel/syscall.c

@@ -0,0 +1,20 @@
+#include <stdarg.h>
+#include "../libc/stdio.h"
+#include "syscall.h"
+
+syscall_t syscalls[] = {
+	(syscall_t)printf,
+};
+
+int syscall_handler(int syscall_num, ...)
+{
+	if ((unsigned)syscall_num < sizeof(syscalls)/sizeof(syscall_t))
+	{
+		va_list args;
+		va_start(args, syscall_num);
+		syscalls[syscall_num](va_arg(args, const char*));
+		va_end(args);
+		return 0;
+	}
+	return -1;
+}

src/kernel/syscall.h

@@ -0,0 +1,8 @@
+#ifndef SYSCALL_H
+#define SYSCALL_H
+
+#define SYSCALL_PRINTF 0
+
+typedef void (*syscall_t)();
+
+#endif

src/programs/hello.c

@@ -1,8 +1,9 @@
-#include "../libc/stdio.h"
-#include "../drivers/serial.h"
+void user_printf(const char* format) {
+    asm volatile ("int $0x80" : : "a"(1), "b"(format));
+}
 
 void main()
 {
-	serial_printf(3, "Hello, world, from a PROGRAM!\n");
+	user_printf("Hello, world, from a PROGRAM!\n");
 	return;
 }